1. Field of the Invention
The present invention generally relates to tubular connections. In particular, the present invention relates to a method of connecting tubulars in such a way that the connection is prevented from becoming unmade in response to expansion of the tubulars. More particularly, the present invention relates to tubular connections that use a connector to mechanically mate a box end of a first tubular with a pin end of a second tubular.
2. Description of the Related Art
In order to access hydrocarbons in subsurface formations, it is typically necessary to drill a bore into the earth. The process of drilling a borehole and of subsequently completing the borehole in order to form a wellbore requires the use of various tubular strings. These tubulars are typically run downhole where the mechanical and seal integrity of the jointed connections are critically important in the original make-up of the tubulars, during expansion of the tubulars, and after expansion of the tubulars.
Typically threaded connections are used to connect multiple tubular members end-to-end. This is usually accomplished by providing tubulars that have a simple male to female threaded connection. The male end is generally referred to as a pin, and the female end as a box. The tubulars are connected, or “made-up,” by transmitting torque against one of the tubulars while the other tubular is typically held stationary. Torque is transmitted in a single direction in accordance with the direction corresponding with connection make-up. Any torque applied to the joint in the make-up direction will have the effect of continuing to tighten the threaded joint.
When running tubulars there is sometimes a requirement to run jointed tubulars that will later be expanded by various types of expansion mechanisms. The most basic type of expander tool employs a simple cone-shaped body which is run into a wellbore at the bottom of the casing which is to be expanded. The expander tool is then forced upward in the wellbore by both pulling on the working string from the surface and applying pressure below the cone. A basic arrangement of a conical expander tool is disclosed in U.S. Pat. No. 5,348,095, issued to Worrall, et al., in 1994 and that patent is incorporated herein in its entirety. Pulling the expanded conical tool has the effect of expanding a portion of a tubular into sealed engagement with a surrounding formation wall, thereby sealing off the annular region therebetween. More recently, rotary expander tools have been developed. Rotary expander tools employ one or more rows of compliant rollers which are urged outwardly from a body of the expander tool in order to engage and to expand the surrounding tubular. The expander tool is rotated downhole so that the actuated rollers can act against the inner surface of the tubular to be expanded in order to expand the tubular body circumferentially. Radial expander tools are described in U.S. Pat. No. 6,457,532 and that patent is incorporated herein by reference in its entirety.
Tubulars to be later expanded are typically run downhole where the mechanical and seal integrity of the connections, or joints, are critically important both in the original and expanded state of the tubulars. The current method of making-up expandable tubulars is by the design of modified threaded connections which can be applied and handled in the same way as conventional oil-field tubulars, i.e., stabbed into each other and screwed together by right hand or left hand rotation and finally torqued to establish the seal integrity. This method of connecting tubulars, though a reliable means of connecting non-expanding tubulars, is proving to be problematic when these tubulars are expanded. The reasons for this being mainly due to the changes in geometry of the connection during expansion due to the stresses applied at the threads, or joint area. For instance, conventional tubulars expanded at the joint may disengage allowing the lower tubing to fall into the wellbore.
It is well known and understood that during the expansion of solid all tubulars, the material in the tubing wall is plastically deformed in more than just the circumferential sense. In order for a tubular to increase in diameter by plastic deformation, the material to make-up the additional circumferential section of wall in the larger diameter must come from the tubing wall itself either by reduction in wall thickness or by reduction in tubular length or a combination of both. In a plain wall section of the tubular this process will normally take place in a relatively controlled and uniform way. However, at the point of a threaded connection, or joint, the changes in wall section, which are required in order to form an expandable threaded connection, introduce very complex and non-uniform stresses during and after expansion. These during-expansion stresses significantly change the thread form and compromise the connection integrity both in terms of its mechanical strength as well as in terms of its sealing capability. Specifically, elongation along the thread helix may result in a thinning of the thread profile perpendicular to the thread helix.
Additionally, due to the changes in geometry of the threads during expansion, thread jumping may also be an issue. Further, the larger elastic deformation caused by the reduced sections of the tubing wall at the roots of the thread will introduce much higher stresses than in other areas of the expanded tubular. This in turn may lead to joint failure due to these stresses approaching or exceeding the ultimate strength of the tubing material or by introduction of short cycle fatigue caused by the cyclic nature of some expansion processes being applied at these high stress levels.
Therefore, there exists a need for a tubular connection that can withstand torque and is prevented from becoming unmade during expansion of the tubular. There exists a further need for a connection that has a higher yield strength than that of the tubular body, or pipe wall. There exists still a further need for a connection that is free to move along its profile relative to the tubular wall during expansion of the tubular.